Two-stage carburetor



June 6, 1956 w. E. EGERER TWQ-STAGE CARBURETOR Filed Jan. 20, 1954 RUIJT @W NW William EEyEIBI IN V EN TOR.

United States Patent O TWO-STAGE CARBURETGR William E. Egerer, Detroit, Mich., assignor t Holley Carburetor Company, Detroit, Mich., a corporation of 'chigan Application January 20, 1954, Serial No. 405,160

1 Claim. (Cl. 261-23) The object of this invention is to facilitate the transition from the first to the second stage of a two-stage carburetor.

So many of the 1954 cars, especially those of the larger size, are now equipped with carburetors of this type, the reason apparently being that by having a smaller car buretor for normal operation they can avoid restricting the performance at high speed by bringing in a second carburetor. In the event that the car is equipped with automatic transmission this transition may be made mechanically. However, many of these larger cars are chauffeur driven and the ordinary synchromesh transmissions are then preferred. With the ordinary synchromesh transmission it is possible to operate at high open throttle low engine speed. When so operating performance would be poor because the flow through the venturi would be too weak to give the necessary fuel air ratio to give rapid acceleration. To avoid this, the second stage is brought in automatically, that is at a time dependent on the flow of air through the main primary venturi. The moment this flow reaches a certain value the opening of the second stage throttle reduces the flow through the primary venturi so that an unsatisfactory state of affairs occurs.

This premature opening of the second stage must be prevented but once the second stage throttle has started to move it should continue to move smoothly.

The figure shows the preferred form of my invention.

In the figure:

19 is the primary venturi;

12 is the secondary venturi;

14 is the fuel nozzle of the first stage;

16 is the fuel nozzle of the second stage;

18 is the choke valve in the primary venturi;

20 is the outlet of the fuel nozzle 14 around which the choke 18 rotates on a shaft 19;

22 is an opening in the venturi leading to the chamber 24 through a passage 21. This chamber is enclosed to the left by the cover 26 and to the right by a flexible diaphragm 28;

Compression spring 30 pushes this diaphragm 28 over to the right;

32 is a link pivotally connected to 34 through a pin 33;

Link 34 is mounted on pin 36 which projects from the outside body of the carburetor;

Pin 38 is in the lower portion of the link 34; this pin 38 rides on the contour 48 on the left of the loose lever 40. Now this pin 38 first rides on the corner and then on to the contour 48, hence it takes quite an eifort to make the first move.

47 is a link from pin 38 to lever 49 through pin 51; lever 49 is locked to throttle shaft 44;

The eccentric throttle 46 is mounted on the throttle shaft 44-, the left hand upstream lip being longer than the downstream right hand lip and the loose lever 40 ice is loosely mounted on the throttle shaft 44 between the lever 49 and the throttle body 53;

The remaining parts are common to all other two-stage carburetors;

Sil is the main or manually controlled throttle of the first stage;

52 is the first stage throttle shaft to which the throttle 58 is locked;

54 is the throttle lever and 56 is a curved link the upper left hand end of which engages a slot 58 of the throttle lever 60 of the second stage.

The only object of this link 56, slot 58 and throttle lever 60 is to provide a safety device to positively force the second stage throttle 46 shut whenever the first stage throttle 50 is put in its idling position as shown. When in its idling position low speed fuel descends through the passage 62 and another opening controlled by needle 66 which is the low speed fuel adjustment. There is another low speed adjustment which is a stop to prevent the throttle 50 being completely closed.

68 and 7 0 are additional low fuel outlets, but of course, they are a common feature of all modern carburetors.

Operation As the throttle 50 opens anti-clockwise, throttle 46 remains closed as the link 56 slides in the slot 58, and the throttle is held closed by the atmospheric pressure acting on the upstream lip on the throttle 46. Suction rises in venturi 10 and in the chamber 24 through the passage 21 and eventually the spring 30 is overcome by the atmospheric pressure acting to the right of diaphragm 28. However, the throttle 46 wont open until the suction is high enough in the chamber 24 to overcome three forces:

1. Spring 30;

2. Coil spring 42;

3. Atmospheric pressure on the left hand side of throttle 46.

Hence, once the pin 38 is over the hump and rides on the curved surface 48 there is a sudden reduction in the force opposing the suction created in the venturi 10, the throttle 46 thus continues to open smoothly and the operation of the car is satisfactory, the reason being that although the suction in the venturi 10 falls rapidly it does not fall far enough to permit the throttle 46 to return to its closed position.

What I claim is:

In a two-stage carburetor having a first stage throttle and a second stage throttle and the usual one-way connection from the first stage to the second stage throttle, comprising a first stage throttle lever, a second stage throttle lever having a slot, a link from the first throttle lever engaging the second throttle lever through said slot so that the second stage throttle is positively closed when the first stage throttle is closed but the first stage throttle may be opened without opening the second stage throttle, suction operated means for opening the second stage throttle including means for delaying the opening of the second stage throttle comprising a venturi in the first stage, a passage therefrom, a vacuum chamber connected thereto, a cover therefor, a diaphragm forming the other wall of said chamber, a lever pivoted on the body of said second stage carburetor, a link extending from said diaphragm connected to one end of said body lever, a second lever mounted on the second stage throttle shaft which is loose thereon, a third second stage throttle lever fixed to said shaft, a pivot pin on the other end of said body lever, a link connected thereto and to said third second stage throttle lever, a contoured surface on the side of said loose lever, spring means tending to rotate said loose lever so that said contoured surface engages said pivot pin, the contour being such that considerable suction must be created in said primary venturi before said diaphragm can overcome said spring means, but less is required to hold the secondary throttle open. V

References Cited in the file of thispatent UNITED STATES PATENTS 

